Are you sure you have it set up properly? For instance, do you have your sensor bar on the top of the screen and its set up calls for the bottom of the screen? Because that can really mess up your aim.
If that's the case, then all you need to do is adjust your sensor bar settings.

I have a big screen (that's Sony too, actually), and other than some pixilation because it's HD, my Wii works fine on it.